Etching method and etching apparatus

ABSTRACT

An etching method is provided. In the etching method, a temperature of a chiller configured to cool a pedestal is controlled so as to become −20 degrees C. or lower. Plasma is generated from a hydrogen-containing gas and a fluoride-containing gas supplied from a gas supply source by supplying first high frequency power having a first frequency supplied to the pedestal from a first high frequency power source. A silicon oxide film deposited on a substrate placed on the pedestal is etched by the generated plasma. Second high frequency power having a second frequency lower than the first frequency of the first high frequency power is supplied to the pedestal from a second high frequency power source in a static eliminating process after the step of etching the silicon oxide film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based upon and claims the benefit of priorityof Japanese Patent Application No. 2014-262859, filed on Dec. 25, 2014,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an etching method and an etchingapparatus.

2. Description of the Related Art

As disclosed in Japanese Laid-Open Patent Application Publication No.7-22393, a method of forming a hole with a high aspect ratio by etchinga silicon oxide film is proposed. For example, Japanese Laid-Open PatentApplication Publication No. 7-22393 discloses a dry etching method forforming an opening with a high aspect ratio and preventing the film fromdepositing on an inner wall of a chamber to reduce a period of timerequired for a cleaning process of an etching apparatus.

Moreover, as an example of the method of forming the hole with the highaspect ratio in the silicon oxide film by etching, a technique isproposed of forming the hole by etching the film while usingC₄F₈/C₄F₆/Ar/O₂ containing gas and keeping a temperature of a wafer highso as to deposit a reaction product on the opening of the hole as littleas possible.

However, in the etching to form a hole or a trench with a high aspectratio, depth loading, which is a phenomenon in which the etching doesnot progress at the bottom of the hole or the trench, occurs as theetching progresses. The depth loading is likely to occur as the aspectratio becomes high.

SUMMARY OF THE INVENTION

Accordingly, in response to the above discussed problems, embodiments ofthe present invention aim to provide an etching method and an etchingapparatus that prevent depth loading and increase an etching rate whenetching a silicon oxide film.

According to one embodiment of the present invention, there is providedan etching method. In the etching method, a temperature of a chillerconfigured to cool a pedestal is controlled so as to become −20 degreesC. or lower. Plasma is generated from a hydrogen-containing gas and afluoride-containing gas supplied from a gas supply source by supplyingfirst high frequency power having a first frequency supplied to thepedestal from a first high frequency power source. A silicon oxide filmdeposited on a substrate placed on the pedestal is etched by thegenerated plasma. Second high frequency power having a second frequencylower than the first frequency of the first high frequency power issupplied to the pedestal from a second high frequency power source in astatic eliminating process after the step of etching the silicon oxidefilm.

According to another embodiment of the present invention, there isprovided an etching apparatus including a chiller configured to controla temperature of a cooling medium so as to keep the temperature at −20degrees C. or lower in order to cool a pedestal. An electrostatic chuckmade of titanium is provided on the pedestal and configured to hold asubstrate thereon. A gas supply source is provided to supply ahydrogen-containing gas and a fluoride-containing gas to the pedestal. Afirst high frequency power source is configured to supply firstfrequency power to the pedestal so as to generate plasma from thehydrogen-containing gas and the fluoride-containing gas and to cause asilicon oxide film deposited on the substrate to be etched by theplasma.

Additional objects and advantages of the embodiments are set forth inpart in the description which follows, and in part will become obviousfrom the description, or may be learned by practice of the invention.The objects and advantages of the invention will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory and are not restrictive of the invention asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of an etching apparatusaccording to an embodiment of the present invention;

FIG. 2 is a graph showing an example of a relationship between an amountof hydrogen gas and an etching rate at an extremely low temperatureaccording to an embodiment of the present invention;

FIG. 3 is a graph showing a vapor pressure curve;

FIG. 4 is a graph showing an example of a relationship between an aspectratio and an etching rate at an extremely low temperature;

FIG. 5 is a diagram showing an example of a result of an etching processaccording to an embodiment of the present invention;

FIGS. 6A and 6B are graphs illustrating an example of an etching processand a static eliminating process according to an embodiment of thepresent invention;

FIG. 7 is a diagram showing a result of an example of an etching processperformed at a high temperature;

FIG. 8 is a diagram showing a result of an example of an etching processat an extremely low temperature according to an embodiment of thepresent invention;

FIG. 9 is a graph showing an example of a relationship between materialsof an electrostatic chuck and a temperature of a wafer according to anembodiment; and

FIG. 10 is a graph showing an example of a relationship between apressure of a heat transfer gas and a temperature of a wafer accordingto an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description is given below of embodiments of the present invention,with reference to accompanying drawings. Note that elements havingsubstantially the same functions or features may be given the samereference numerals and overlapping descriptions thereof may be omitted.

[Overall Configuration of Etching Processing Apparatus]

To begin with, a description is given below of an etching apparatus 1according to an embodiment of the present invention with reference toFIG. 1. FIG. 1 illustrates an example of a vertical cross section of theetching apparatus 1 according to the embodiment. The etching apparatus 1of the embodiment is configured to be a parallel plate type plasmaprocessing apparatus (capacitively-coupled plasma processing apparatus)including a pedestal 20 and a gas shower head 25 that are disposed to beparallel with each other in a chamber 10. The pedestal 20 also functionsas a lower electrode, and the gas shower head 25 also functions as anupper electrode.

The etching apparatus 1 includes the chamber 10 with a surface, forexample, made of alumited (anodized) aluminum. The reaction chamber 10is connected to the ground. The pedestal 20 is installed on a bottom ofthe chamber and receives a semiconductor wafer (which is hereinafterjust called a “wafer W”) thereon. The wafer W is an example of asubstrate that is an object subject to be etched, and includes a maskfilm on a silicon oxide film formed thereon.

The pedestal 20 is, for example, made of aluminum (Al), titanium (Ti),silicon carbide (SiC) and the like. An electrostatic chuck 106 forelectrostatically attracting the wafer W thereon is provided on an uppersurface of the pedestal 20. The electrostatic chuck 106 is configured tohave a chuck electrode 106 a sandwiched between insulating bodies 106 bor surrounded by the insulating body 106 b. A direct voltage source 112is connected to the chuck electrode 106 a, and attracts the wafer W onthe electrostatic chuck 106 by Coulomb's force by applying a directvoltage HV to the chuck electrode 106 a.

The pedestal 20 is supported by a support 104. A refrigerant passage 104a is formed inside the support 104. A refrigerant inlet pipe 104 b and arefrigerant outlet pipe 104 c are connected to the refrigerant passage104. A cooling medium output from a chiller 107 such as cooling waterand brine circulates through the refrigerant inlet pipe 104 b, therefrigerant passage 104 a and the refrigerant outlet pipe 104 c. Thiscauses the pedestal 20 and the electrostatic chuck 106 to be cooled.

A heat transfer gas supply source 85 supplies a heat transfer gas suchas helium gas (He) or argon gas (Ar) to a back surface of the wafer W onthe electrostatic chuck 106 through a gas supply line 130. Such aconfiguration allows a temperature of the electrostatic chuck 106 to becontrolled by the cooling water flowing through the refrigerant passage104 a and the heat transfer gas supplied to the back surface of thewafer W. As a result, the wafer W can be controlled so as to become apredetermined temperature.

A power supply device 30 for supplying superimposed power of twofrequencies is connected to the pedestal 20. The power supply device 30includes a first high frequency power source 32 that supplies first highfrequency power (high frequency power for generating plasma) of a firstfrequency and a second high frequency power source 34 for supplyingsecond high frequency power (high frequency power for generating a biasvoltage) of a second frequency. The first high frequency power source 32is electrically connected to the pedestal 20 through a first matchingbox 33. The second high frequency power source 34 is electricallyconnected to the lower electrode 20 through a second matching box 35.For example, the first high frequency power source 32 supplies the firsthigh frequency power of 40 MHz to the pedestal 20. For example, thesecond high frequency power source 34 supplies the second high frequencypower of 0.3 MHz to the pedestal 20. Here, although the first highfrequency power is supplied to the pedestal 20 in the embodiment, thefirst high frequency power may be supplied to the gas shower head 25.

The first matching box 33 causes load impedance of the first highfrequency power source 32 to match internal (or output) impedancethereof. The second matching box 34 causes load impedance of the secondhigh frequency power source 34 to match internal (or output) impedancethereof. The first matching box 33 functions to cause the load impedanceof the first high frequency power source 32 to appear the same as theinternal impedance thereof when plasma is generated in the chamber 10.The second matching box 35 functions to cause the load impedance of thesecond high frequency power source 34 to appear the same as the internalimpedance thereof when plasma is generated in the chamber 10.

The gas shower head 25 is attached to the chamber 10 through a shieldring 40 covering a peripheral side wall thereof so as to close anopening of a ceiling part of the chamber 10. The gas shower head 25 maybe electrically grounded as illustrated in FIG. 1. Moreover, byconnecting a variable direct current power source to the shower head 25,a predetermined direct current (DC) voltage may be applied to the showerhead 25.

A gas introduction port 45 for introducing a gas is formed in the gasshower head 25. A diffusion chamber 50 a located on a central side and adiffusion chamber 50 b located on an edge side for diffusing a gasdiverged from the gas introduction port 45 and introduced thereto areprovided inside the gas shower head 25. The gas supplied from a gassupply source 15 is supplied to the diffusion chambers 50 a and 50 bthrough the gas introduction port 45, and diffuses across each of thediffusion chambers 50 a and 50 b. Then, the gas is introduced toward thepedestal 20 from many gas supply holes 55.

An exhaust opening 60 is formed in a bottom surface of the chamber 10,and the chamber 10 is evacuated by an exhaust device 65 connected to theexhaust opening 60. This enables the inside of the chamber 10 to bemaintained at a predetermined degree of vacuum. A gate valve G isprovided at a side wall 102 of the chamber 10. The gate valve G opensand closes a carry-in/out opening when carrying the wafer in/out of thechamber 10.

The etching apparatus 1 includes a control unit 100 configured tocontrol the operation of the entire apparatus. The control unit 100includes a CPU (Central Processing Unit) 105, a ROM (Read Only Memory)110 and a RAM (Random Access Memory) 115. The CPU 105 performs a desiredprocess such as the etching process and the static eliminating processdescribed later in accordance with a recipe stored in these memoryareas. The recipe specifies control information of the apparatuscorresponding to process conditions such as process time, a pressure(evacuation of the gas), high frequency power and voltage, various gasflow rates, temperatures inside the chamber 10 (an upper electrodetemperature, a side wall temperature of the chamber 10, a temperature ofthe electrostatic chuck 106 and the like), and a temperature of thechiller 107. Here, the recipe specifying programs and process conditionsthereof may be stored in a hard disk or a semiconductor memory.Furthermore, the recipe may be set in a predetermined position of thememory area in a state of being stored in a portable computer readablestorage medium such as a CD-ROM, a DVD and the like.

When performing an etching process, open and close of the gate valve Gis controlled, and a wafer W is carried in the chamber 10 and placed onthe pedestal 20. The direct current voltage source 12 applies a directcurrent voltage HV to the chuck electrode 106 a, thereby attracting andholding the wafer W on the electrostatic chuck 106 a by Coulomb's force.

Next, a gas for etching and high frequency power are supplied to thechamber 10, thereby generating plasma. A plasma etching process isperformed on the wafer by the generated plasma.

After the etching process, the direct current voltage source 112 appliesa DC voltage HV having an opposite sign to the DC voltage applied to thechuck electrode 106 a while attracting the wafer W to the chuckelectrode 106 a in order to eliminate the charge of the wafer W, therebyremoving the wafer W from the electrostatic chuck 106. The open andclose of the gate valve G is controlled, and the wafer W is carried outof the chamber 10.

[Etching Process]

Next, a description is given below of an etching process on a siliconoxide film (SiO₂) performed by the etching apparatus 1 having such aconfiguration according to the embodiment. When forming a hole or atrench having a high aspect ratio into the silicon oxide film, there isprovided an etching method of forming the hole by using, for example,C₄F₈/C₄F₆/Ar/O₂ containing gas, and by setting a temperature of thewafer W at a high temperature so as to deposit a reaction product on anopening of the hole as little as possible.

However, in the hole and the trench having the high aspect ratio, adepth loading occurs as the etching progresses. Moreover, the depthloading is likely to occur as the aspect ratio increases. Because ofthis, according to the above etching method, the etching may notprogress when forming a hole having a higher aspect ratio in the future.

Therefore, the etching apparatus 1 according to the embodiment providesan etching method for preventing the depth loading and improving anetching rate when etching the silicon oxide film.

Experiment 1

In the etching process according to the embodiment, the silicon oxidefilm is etched in an extremely low temperature process having a controltemperature of the chiller 107 of −20 degrees C. or lower whilesupplying a hydrogen-containing gas and a fluoride-containing gas intothe chamber 10. In an experiment 1, CF₄ gas was used as an example ofthe fluoride-containing gas and H₂ gas was used as an example of thehydrogen-containing gas.

FIG. 2 shows a result of the experiment 1 of the etching processaccording to the embodiment. FIG. 2 shows an extremely low temperatureprocess setting a temperature of the cooling medium supplied from thechiller 107 at −20 degrees C., an extremely low temperature processsetting the temperature of the cooling medium supplied from the chiller107 at −60 degrees C., and a room temperature process setting thetemperature of the chiller 107 at 20 degrees C. In any case, CF₄ gas andH₂ gas were supplied into the chamber 10. In order to measure an etchingrate of the silicon oxide film when increasing a partial pressure of H₂gas relative to CF₄ gas, the experiment 1 showed an etching rate whenincreasing a flow rate of H₂ gas while keeping a flow rate of CF₄ gasconstant.

According to a result of the experiment 1, in the extremely lowtemperature processes setting the temperature of the chiller 107 at −20degrees C. and −60 degrees C., when the partial pressure of H₂ gasrelative to CF₄ gas increased, the etching rate increased up to apredetermined partial pressure. On the other hand, in the roomtemperature process setting the temperature of the electrostatic chuck106 at 20 degrees C., the etching rate decreased as the partial pressureof H₂ gas relative to CF₄ gas increased.

Hence, in the etching process of the embodiment, the etching isperformed by using H₂ gas and CF₄ gas, setting an appropriate partialpressure of H₂ gas relative to CF₄ gas, and setting the temperature ofthe chiller 107 at the extremely low temperature of −20 degrees C. orlower. This enables the etching rate to be increased. In particular, aninflection point indicating the etching rate became higher at and around−60 degrees C., and the etching rate is estimated to further becomehigher around a temperature lower than −60 degrees C.

Here, in the extremely low temperature process, the etching rateincreased halfway and decreased therefrom when the partial pressure ofH₂ gas increased. This is thought to be because an amount of F of CF₄gas relative to H₂ gas decreases, which causes the etching to beunlikely to progress and reduces the etching rate.

(Analysis of Phenomenon)

In the etching process of the embodiment, H₂ gas is supplied as anexample of the hydrogen-containing gas, and CF₄ is supplied as anexample of the fluoride-containing gas. As a result of the etching ofthe silicon oxide film by H₂ gas, H₂O is generated as a reactionproduct. As shown by a vapor pressure curve, H₂O has a low saturatedvapor pressure. A solid line in FIG. 3 indicates an experimental value,and a broken line indicates a calculated value. A state on the vaporpressure curve is a mixed state of a liquid and a gas.

When the temperature of the chiller 107 is set at a low temperature of−20 degrees C., or preferably at an extremely low temperature of −60degrees C. while keeping the pressure at 8.0 Pa (60 m Torr) during theetching, H₂O on a surface of the silicon oxide film is saturated andpresent in a state of a liquid.

The liquid present on the surface of the silicon oxide film alsocontains HF-based radicals generated from CF₄ gas by reaction inaddition to water of the reaction product. Because of this, hydrofluoricacid (HF) is generated by reaction of the HF-based radicals and water.Hydrofluoric acid dissolved in water on the surface of the silicon oxidefilm mainly urges the etching by chemical reaction, and the etching ratespecifically increases. In the etching process of the embodiment, plasmaconditions other than the temperature of the electrostatic chuck 106 donot change. Hence, the etching rate is thought to improve mainly bychemical reaction due to an action of the liquid of hydrofluoric acidpresent on the surface of the silicon oxide film.

Experiment 2

FIG. 4 shows a relationship between an aspect ratio and an etching rateof a silicon oxide film as a result of an experiment 2 about the etchingprocess of the embodiment. In the experiment 2, extremely lowtemperature process conditions in the etching process of the embodimentare as follows: a temperature of the chiller 107 was −60 degrees C., andgas types were CF₄ gas/H₂ gas. Room temperature process conditions of acomparative example were as follows: a temperature of the chiller 107was 20 degrees C., and gas types were C₄Fe/C₄F₆/Ar/O₂.

The result indicates that the etching rate in the extremely lowtemperature process was two or more times higher than the etching ratein the room temperature process. This is because CF₄ gas used in theetching process of the embodiment is a low molecular weight gas and theradicals of CF₄ are more likely to reach the bottom of the hole thanhigh molecular weight gases such as C₄F₈ gas and C₄F₆ used in thecomparative example.

Furthermore, as discussed above, another reason for the above is thatthe reaction product is unlikely to deposit on the opening of the holeby the chemical reaction on the surface of the silicon oxide film in theetching process of the embodiment, and the etching progresses in a stateunlikely to close the opening of the hole. For these reasons, in theetching process of the embodiment, the hole with a high aspect ratio canbe formed.

FIG. 5 shows an example of a vertical cross section of an etching shapeof the hole formed as a result from the etching process of theexperiment 2.

Here, the silicon oxide film was etched by using a masking film of anamorphous carbon layer (ACL). As a result of the etching, in the case ofextremely low temperature process setting the temperature of the chiller107 at −60 degrees C., the etching rate (E/R) became higher than theetching rate of the room temperature process, and mask selectivity (Sel)also became much better than the mask selectivity of the roomtemperature process. Thus, according to the etching method of theembodiment, the etching rate can be improved while suppressing the depthloading.

As described above, according to the etching method of the embodiment,by using CF₄ gas/H₂ gas as the gas species and by performing theextremely low temperature process setting the temperature of the chiller107 at −20 degrees C. or lower (preferably −60 degrees C. or lower), thedepth loading can be improved, and the etching rate and the maskselectivity can be increased.

The etching process of the embodiment can be applied to the etching ofthe silicon oxide film in manufacture of a three-dimensional stackedmultilayer semiconductor memory such as 3D NAND flash memory. In thiscase, a hole and a trench with a high aspect ratio can be formed in thesilicon oxide film and a stacked multilayer film containing the siliconoxide film by increasing the etching rate while suppressing the depthloading. In addition, the etching process of the embodiment can beapplied to a multilayer stacked structure of an oxide film and anitriding film and a multilayer stacked structure of the oxide film anda poly silicon film.

Here, an etching process by an extremely low temperature process usinghydrofluorocarbon (HFC) may be performed by supplying H₂ gas as anexample of the hydrogen-containing gas and supplying nitrogentrifluoride gas as an example of the fluoride-containing gas.

[Static Eliminating Process]

Next, a description is given below of a static eliminating processperformed when carrying a processed wafer W out of the chamber 10 afterperforming the etching process of the embodiment with reference to FIG.6.

In the etching process of the embodiment, the silicon oxide film isetched by setting the temperature of the chiller 107 at an extremely lowtemperature in a range from −20 degrees C. to −60 degrees C. Due tothis, the processed wafer W has a low temperature, and is carried out ofthe etching apparatus 1. Then, the processed wafer W is exposed to theatmosphere while being transferred to a FOUP (Front-Opening UnifiedPod), during which condensation occurs on a surface of the wafer W.

As a method of preventing the condensation on the surface of the waferW, carrying the wafer W out of the etching apparatus 1 after holding thewafer W in a load lock chamber (LLM, load lock module) for a few orseveral minutes, or transferring the wafer W to the FOUP after heatingthe wafer W by providing another heater, is considered.

However, when the wafer W is held for a few or several minutes,throughput of the entire process decreases. Also, when heating the waferW by providing the heater, installing the heater is needed in additionto the decrease of the throughput, thereby increasing the cost.

Therefore, in the etching apparatus 1 of the embodiment, the temperatureof the wafer W is quickly raised in the chamber 10 during the staticeliminating process.

FIG. 6A illustrates a comparative example of the static eliminatingprocess. FIG. 6B illustrates an example of a static eliminating processperformed in the etching apparatus 1 according to an embodiment.

In FIGS. 6A and 6B, when the etching process (expressed as “Process” inFIGS. 6A and 6B) ends, the static eliminating process (“T1” and “T2” inFIGS. 6A and 6B) is performed.

In the static eliminating process of FIG. 6A, the supply of the firsthigh frequency power HF and the second high frequency power LF isstopped after finishing the etching process. Next, in the staticeliminating process in FIG. 6A, weak plasma is generated by supplyingthe first high frequency power HF (e.g., frequency is 13.56 MHz) havinga relatively low power of about 300 W at time T2 after the elapse oftime T1, and the weak plasma is caused to act on the wafer W. Thiscauses the charge on the surface of the wafer W to discharge toward theplasma.

After that, the direct current voltage source 112 applies a minus DCvoltage HV (−3000 V) having the opposite sign to the applied plus DCvoltage while attracting the wafer W on the chuck electrode 106 a to thechuck electrode 106 a and eliminates the static charge from the wafer W,thereby removing the wafer W from the electrostatic chuck 106. After theelapse of the static eliminating process time T2, the application of thefirst high frequency power HF and the second high frequency power HV isstopped, and the static eliminating process finishes.

In the static eliminating process of the embodiment shown in FIG. 6B,the supply of the first high frequency power HF and the second highfrequency power LF is stopped when finishing the etching process. Next,in the static eliminating process in FIG. 6B, week plasma is generatedby supplying the first high frequency power HF having relatively lowerpower of about 300 W to the pedestal 20 at time T2 after the elapse oftime T1, and the weak plasma is caused to act on the wafer W so as todischarge the charge on the surface of the wafer W toward the plasma.The process up to here is the same as the static eliminating process ofFIG. 6A.

After that, in the static eliminating process of FIG. 6B, the secondhigh frequency power LF of 500 W is supplied to the pedestal 20. Thisallows the temperature of the wafer W to be raised while removing thewafer W from the electrostatic chuck 106. In other words, in theembodiment, the second high frequency power LF is supplied to thepedestal 20 in addition to the first high frequency power HF whenremoving the wafer W from the electrostatic chuck 106, therebyincreasing an amount of incident ions and the temperature of the wafer Wrapidly.

Furthermore, as illustrated in FIG. 6B, when supplying the second highfrequency power HF, the ion energy is increased by increasing not onlythe amount of incident ions but also the first frequency power from 300W to 500 W. In other words, in the embodiment, considering an increaseof damage to the wafer W due to the supply of the second high frequencypower LF, the first high frequency power HF is increased when supplyingthe second high frequency power LF to the pedestal 20. This causes theion energy to increase so as not to increase the amount of incident ionson the wafer W more than necessary, which makes it possible to minimizethe damage to the wafer W. Here, the first high frequency power HF mayremain 300 W when supplying the second high frequency power LF.

According to this method, rapidly increasing the temperature of thewafer W is possible while maintaining the throughput without installinga special new component or a new function in the etching apparatus 1. Inaddition to this, blowing dried air to a gap inside the chamber 10(portion exposed to the atmosphere) is preferable in order to preventthe condensation of the wafer W during the transfer.

[Material of Electrostatic Chuck]

Next, a description is given below of the electrostatic chuck 106 usedin the etching apparatus 1 according to an embodiment with reference toFIGS. 7 through 10. FIGS. 7 and 8 show results of examples of etchingprocesses performed by using an apparatus A (which has the sameconfiguration as the etching apparatus of FIG. 1) and an apparatus B(which is configured to include a magnet outside the chamber 10 of theetching apparatus 1 of FIG. 1, thereby controlling plasma). In FIGS. 7and 8, a film to be etched is a stacked multilayer film of a maskingfilm (poly silicon film), a silicon nitride film (SiN), and a siliconoxide film (SiO₂). Holes with a high aspect ratio are formed in thesilicon nitride film and the silicon oxide film by the etching processof the embodiment.

In the apparatus A and the apparatus B of FIG. 7, the electrostaticchucks 106 are made of aluminum. FIG. 7 shows a result of an example ofan etching process of a high temperature process according to acomparative example, and for example, process conditions of theapparatus A and the apparatus B are shown in the following.

Process Conditions of Etching Process: <Apparatus A>

Gas Type: C₄F₈/CH₂F₂/O₂Temperature of Chiller: 60 degrees C.Pressure: 15 mTorr (2.0 Pa)

<Apparatus B>

Gas Type: C₄F₆/CH₂F₂/O₂Temperature of Chiller: 60 degrees C.Pressure: 15 mTorr (2.0 Pa)

In the apparatus A and the apparatus B used in the process of FIG. 8,the electrostatic chucks 106 are made of aluminum or titanium. FIG. 8shows a result of an example of an etching process of the extremely lowtemperature process according to the embodiment. For example, processconditions of the apparatus A and the apparatus B are shown in thefollowing.

Process Conditions of Etching Process <Apparatus A>

Gas Type: CF₄/H₂Temperature of Chiller: −60 degrees C.Pressure: 60 mTorr (8.0 Pa)

Here, the etching result of the apparatus A on the right side was thecase where the electrostatic chuck 106 was made of titanium, and theheat transfer gas of helium (He) at a pressure of 40 Torr (5352 Pa) wassupplied. The etching result of the apparatus A on the left side was thecase where the electrostatic chuck 106 was made of titanium and the heattransfer gas is not supplied.

<Apparatus B>

Gas Type: CF₄/H₂Temperature of Chiller: −60 degrees C.Pressure: 60 mTorr (8.0 Pa)

Here, the etching result of the apparatus B on the right side was thecase where the electrostatic chuck 106 was made of titanium, and theetching result of the apparatus B on the left side was the case wherethe electrostatic chuck 106 was made of titanium. In both of the cases,the heat transfer gas is not supplied.

As a result, in the etching process of the extremely low temperatureprocess according to the embodiment, it is noted that the depths of theetching of the silicon nitride film and the silicon oxide film (“SiN+OxDepth” in FIGS. 7 and 8) are deeper than the depths of the etching inthe etching process of the high temperature process shown in FIG. 7.Thus, in the etching process of the extremely low temperature processaccording to the embodiment, preventing the depth loading and etchingthe film with the high aspect ratio are possible compared to the etchingprocess of the high temperature process shown in FIG. 7.

Moreover, as shown in FIG. 8, the etching rate is higher when using theelectrostatic chuck made of aluminum than when using the electrostaticchuck made of titanium. In order to further analyze this result,temperatures of the wafer W were measured when performing the etchingprocess of the extremely low temperature process of the embodiment byusing both of the electrostatic chuck 106 made of titanium and aluminum.FIG. 9 shows the result. Process conditions of the etching process atthat time were shown as follows:

Gas Type: CF₄/H₂Temperature of Chiller: 25 degrees C.Pressure: 60 mTorr (8.0 Pa)

FIG. 9 shows the result of the temperature of the wafer W during theetching process measured at a plurality of points. In the case of theelectrostatic chuck made of aluminum of FIG. 9, the temperatures of thewafer W during the etching process were approximately 40 degrees C.Because the temperature of the chiller 107 was 25 degrees C., thetemperatures of the wafer W were about 15 degrees higher than thetemperature of the chiller 107. From this result, when the temperatureof the chiller 107 is −60 degrees C., the temperature of the wafer W isestimated to become about −45 degrees C.

Similarly, in the case of the electrostatic chuck 106 made of titaniumof FIG. 9, the temperatures of the wafer W during the etching processwere approximately 80 degrees C. Because the temperature of the chiller107 was 25 degrees C., the temperatures of the wafer W were about 55degrees higher than the temperature of the chiller 107. From thisresult, when the temperature of the chiller 107 is −60 degrees C., thetemperature of the wafer W is estimated to become about −5 degrees C.

From the results, in the case of the electrostatic chuck 106 made ofaluminum shown in FIG. 8, the etching rate was higher than that of theelectrostatic chuck made of titanium because the temperature of thewafer W when the electrostatic chuck 106 was made of aluminum could becontrolled so as to become about −45 degrees C. In other words, when theelectrostatic chuck 106 is made of aluminum, the extremely lowtemperature process of the embodiment is performed as long as thetemperature of the chiller 107 is −60 degrees C., which makes itpossible to reduce the depth loading and to increase the etching rate.

In contrast, when the electrostatic chuck 106 was made of titanium,because the temperature of the wafer W became about −15 degrees C. evenwhen the temperature of the chiller 107 was about −60 degrees C., theextremely low temperature process of the embodiment could not beperformed, and the etching rate was not high. Thus, when performing theetching process of the embodiment by using the electrostatic chuck 106made of titanium, the temperature of the chiller 107 is preferablycontrolled so as to become about −100 degrees C. In this case, because alimit value of the cooling medium (brine) of the chiller 107 is about−80 degrees C., liquid nitrogen is preferably used as the cooling mediumin order to perform the etching process of the embodiment by using theelectrostatic chuck 106 made of titanium. When performing the etchingprocess of the embodiment at an extremely low temperature of about −100degrees C., titanium is preferably used in the electrostatic chuck 106.

[Pressure Dependency of Heat Transfer Gas]

Furthermore, in FIG. 8, when titanium was used in the electrostaticchuck 106 and the heat transfer gas was supplied, the etching rate washigher than when the heat transfer gas was not supplied. This is becausean effect of transferring the heat of the wafer W to the electrostaticchuck 106 increased due to an action of the heat transfer gas and thetemperature of the wafer W decreased.

Finally, in the etching process of the silicon oxide film at theextremely low temperature of the embodiment, an experiment for analyzingpressure dependency of the heat transfer gas supplied to the backsurface of the wafer W was performed. The temperature of the chiller 107was set at 25 degrees C. The result was shown in FIG. 10. The left-sidegraph in FIG. 10 shows temperatures of the wafer W when theelectrostatic chuck 106 made of titanium is used and a heat transfer gas(He) is supplied at a pressure of 2000 Pa (15 Torr). Each line shows atemperature change at each of a plurality of locations over the etchingtime.

This result indicates that uniformity of the temperature of the wafer Wacross the surface can be improved when supplying the heat transfer gasat the pressure of 2000 Pa (15 Torr) and at a pressure of 5332 Pa (40Torr). Moreover, the result indicates that the wafer W temperature islower and the uniformity of the wafer W temperature is better whensupplying the heat transfer gas at the pressure of 5332 Pa (40 Torr)than when supplying the heat transfer gas at the pressure of 2000 Pa (15Torr).

Hence, in the etching process of the extremely low temperature accordingto the embodiment, when using the electrostatic chuck made of titanium,the pressure of the heat transfer gas supplied to the back surface ofthe wafer while etching the silicon oxide film is preferably controlledso as to become 2000 Pa (15 Torr).

Thus, according to the etching method and the etching apparatus of theembodiments, the depth loading can be suppressed, and the etching rateof the silicon oxide film can be increased.

Hereinabove, although the etching method and the etching apparatus havebeen described according to the embodiments, the etching method and theetching apparatus of the present invention is not limited to theembodiments and various modifications and improvements can be madewithout departing from the scope of the invention. Moreover, theembodiments and modifications can be combined as long as they are notcontradictory to each other.

For example, the etching process and the static eliminating process ofthe present invention may be applied not only to a capacitively coupledplasma (CCP: Capacitively Coupled Plasma) apparatus but also to othertypes of etching apparatuses. For example, the other types of etchingapparatus includes an inductively coupled plasma (ICP: InductivelyCoupled Plasma) apparatus, a CVD (Chemical Vapor Deposition) apparatususing radial line slot antenna, a helicon wave excited plasma (HWP:Helicon Wave Plasma) apparatus, an electron cyclotron resonance plasma(ECR: Electron Cyclotron Resonance Plasma) apparatus and the like asexamples.

A substrate to be processed in the semiconductor fabrication apparatusof the present invention is not limited to the wafer, but for example,may be a large substrate for a flat panel display, a substrate for an EL(electroluminescence) device or a solar cell.

What is claimed is:
 1. An etching method, comprising: controlling atemperature of a chiller configured to cool a pedestal so as to keep thetemperature at −20 degrees C. or lower; generating plasma from ahydrogen-containing gas and a fluoride-containing gas supplied from agas supply source by supplying first high frequency power having a firstfrequency supplied to the pedestal from a first high frequency powersource; etching a silicon oxide film deposited on a substrate placed onthe pedestal by the generated plasma; and supplying second highfrequency power having a second frequency lower than the first frequencyof the first high frequency power to the pedestal from a second highfrequency power source in a static eliminating process after the step ofetching the silicon oxide film.
 2. The etching method as claimed inclaim 1, wherein the hydrogen-containing gas is hydrogen (H₂) gas, andthe fluoride-containing gas is carbon tetrafluoride (CF₄) gas.
 3. Theetching method as claimed in claim 1, wherein the hydrogen-containinggas is hydrogen (H₂) gas, and the fluoride-containing gas is nitrogentrifluoride (NF₃) gas.
 4. The etching method as claimed in claim 1,wherein the substrate is held on an electrostatic chuck provided on thepedestal, and the electrostatic chuck is made of titanium.
 5. Theetching method as claimed in claim 1, wherein the step of etching thesilicon oxide film deposited on the substrate comprises a step ofsupplying a heat transfer gas to a back surface of the substrate placedon the pedestal, and the heat transfer gas is controlled so as to have apressure of 2000 Pa (15 Torr) or higher.
 6. The etching method asclaimed in claim 1, wherein the temperature of the chiller is controlledso as to become −60 degrees C. or lower.
 7. The etching method asclaimed in claim 1, wherein the step of supplying the second highfrequency power to the pedestal includes a step of supplying the firsthigh frequency power to the pedestal before supplying the second highfrequency power to the pedestal in the static eliminating process. 8.The etching method as claimed in claim 7, wherein the step of supplyingthe second high frequency power to the pedestal further includes a stepof supplying both of the first frequency power and the second frequencypower to the pedestal in a superimposed manner, and the first frequencypower in the step of supplying both of the first frequency power and thesecond frequency power to the pedestal is higher than the firstfrequency power in the step of supplying the first high frequency powerto the pedestal before supplying the second high frequency power to thepedestal in the static eliminating process.
 9. The etching method asclaimed in claim 1, wherein a first partial pressure of thefluoride-containing gas is lower than a second partial pressure of thehydrogen-containing gas.
 10. An etching apparatus, comprising: a chillerconfigured to control a temperature of a cooling medium so as to keepthe temperature at −20 degrees C. or lower in order to cool a pedestal;an electrostatic chuck made of titanium provided on the pedestal andconfigured to hold a substrate thereon; a gas supply source to supply ahydrogen-containing gas and a fluoride-containing gas to the pedestal;and a first high frequency power source configured to supply firstfrequency power to the pedestal so as to generate plasma from thehydrogen-containing gas and the fluoride-containing gas and to cause asilicon oxide film deposited on the substrate to be etched by theplasma.